Stall indicator



Mach 8, 1938.

R. P. HOLLAND, JR

STALL INDI CA'I'OR Filed Nov. 6, 1936 m. w w m QAYMoND P. HOLLANDJR. I

atente Mar. 8, 1938 s'rALL mmoa'roa Raymond P. Holland, In, Kenmore, N;Y., as-

signor to'lCurtiss-Wrightcorporation, a corpo-.

ration of New York Appnmiofnovember s, 1988, senu'no. mania'v 'z cmmz.zer- 1) 'Iv'his invention relatesto aircraft instruments and isparticularly concerned with the provision of an automatic deviceforwarning the aircraft crew when the aircraft may be in dangerousflight attitudes. v i

In the maneuvering of aircraft, a position may be reached which istknownas a ustall" which essentially comprises the aircraft reaching such ahigh angle of attack with respect to the air 10 stream that the lift ofthe wings falls oif rapidly. Normally, the aircraft crew attempts tomaintain aircraft at such a low angle of' attack that the stallingposition will never be reached, but in certain maneuvers, such astake-oil' and landing 15 it is essential that the aircraft be placedinattitudes involving a high angle of attack in lorder to obtain maximumlift from the wings. Since only a small increase in angle of attack isnecessary to shift from a high lift position to a stalled posi- 20 tionwhere the lift isverylow, it is highly desirable to provide some meanswhich will warn the aircraft crew immediately when the angle of attackbecomes critical.

An object of this invention is to provide auto- 25 matic means dependentfor its functioning upon the approach of the aircraft toward a stallingattitude. p

A further object is to provide a slot in the Wing l ading edge of anaircraft which is subject to 30 sitive or negative pressure inaccordance With the angle of attack of the Wing.

A further objectis to provide aura] signalling means responsive tosuction created at the aforementioned slot by reason of a negativepressure 35 existing thereat under wing high angle of attackIconditions.

Still another object is to provide valve means whereby airflow throughthe aforementioned slot may be confined to outward flow When the wing 40is in a high angle of attack attitude.

In the conventional aircraft Wing, in flight, the air pressuredistribution is such that a positive pressure area obtains at the nosepart and under surface of the Wing whereas a negative pressure 45condition exists on the upper part of the Wing and on the upper part ofthe nose of the Wing. There is one point which shifts along the upperpart of the Wing nose in accordance with high angle of attack conditionsWhereat the air pres 50 sure is zero (using normal atmospheric pressureas the datum zero). Under high angle of attack conditions, this zeropoint shifts forwardly,` and under low angle of attack conditions itshifts rearwardly. This shift in the 'zero pressure zone 55 is utilizedin this invention to provide a stali warning indicator to the pilot.VThe particular device and mechanism for the accomplishment of theinvention-arehereafter described in detali and are shown in the annexeddrawing in which:

Flg. 1 is .a perspective view of an aircraft in flight incorporating theprovisions Vof theinvention.

, Fig. 2 is a partial section through a wing lead- Ving edge showingpart'of the stali indicator.

Fig. 3 is a fragmentary plan of a Wing including Vthe device of theinvention.

Fig. 4 is a perspective view of a valve suitable for use with theinvention.

Flgs. 5 and 6 are fragmentary views of the air conduit utilized in theinvention, showing an alternative form of valve respectively. in a closeand open position, and

Figs. 'land are diagrammatic sections of an Aairfoil including pressuredistribution curves thereon respectively in the low and high angle ofattack positions. I i

Referring to Figs. 7 and 8, a conventional airfoil III is shownrespectively in iowand high angle of attack positions. In Fig. 'I itwill be noted that a positive pressure region'exists on the lowersection of the nose and airfoil, while on the upper surface of the Winga low pressure region exists, this 'pressure being lower thanatmospheric. At a point II, on the upper nose portion of the Wing, thepressure shifts from positive to negative whereby at that pointatmospheric pressure will obtain. In Pig. 8, where the airfoil is in ahigh angle of attack position the point of zero or atmospheric pressuredesignated as I I' has moved forwardly. It will thus be seen that thereis a point I2 between the points II and I I' which is subject topositive or negative pressure in accordance with the angle of attack ofthe Wing. In this invention I provide an elongated opening I3 at thepoint Iz which mmmucates with the 40h conduit Id extending through theWing and into the crew compartment IS. In the conduit Il I provide aone-Way valve IS shown in Fig. 4 which comprises a hinged door IGcapable of moving toward or away'from a seat IT, the door I being soarranged that it may open the conduit Il if there is a tendency for airto flow from the cockpit Il toward the slot IJ. If the airiiow tendencyis in the reverse direction, the door` IO will close preventing suchairflow. At the cockpit end ofthe conduit Il I provide some form ofindicating device which in the present embodiment comprises a simple airoperated whistle I 8.'

The operation of the device is as follows:

If the aircraft is flying at low angle of attack 2 aiion'so attitude, asin Fig. '7, positlve pressure will exist at the opening I 3, whereby airwould tend to flow therefrom toward the cockpit II through the duct H.The valve I 5 under this condition closes, to prevent such flow. If theaircraft is maneuvering toward a stalling attitude as in Fig. 8, theopening |3 is moved to a region of less than atmospheric pressure.Consequently, since atmospheric pressure exists in the pilot's cockpit,air will flow from the whistle llthrough the conduit Il and out throughthe opening |3, such.

airfiow opening the valve |5 and causing the whistle |8 to give an auralsignal which immediately warns the pilot that he is approaching astalling condition of the wing. Obviously, the opening I! will belocated at a position on the nose of the wing to cause awarning signalto the pilot before the stalling angle is actually reached, so that theaircraft crew will have an opportunity to correct the aircraft attitudebefore lift is reduced.

In Figs. 5 and 6 I show an alternative form" of valve in the conduit Il,the valve elements comprising resilient pockets IS which normally tendto close the conduit for the prevention of airflow therethrough. Ifhigher pressure exists on theright hand side of the pockets i 9 as shownin the figures, the pockets will seal the conduit from airflow. If theairflow tendency is from the left as shown in Flg. 6 the pockets will becollapsed against the sides of the conduit and airflow will obtain asdesired.

Although in the present embodiment of the invention I prefer to use awhistle IB, as described, the invention is not to be construed aslimited to this form of signal. The tendency for airflow from the cabintoward the wing may be utilized to operate any other form of signalwhich might be deemed desirable.

While I have described my invention in detail in its present preferredembodiment, it will be obvious to those skilled in the art, afterunderstanding my invention, that various changes and modifications maybe made therein without departing from the spirit or scope thereof. Iaim in the appended claims to cover all such modiflcations and changes.

What I claim is:

1. In aircraft including crew quarters and a. wing having azone at theleading edge thereof subject to pressure greater or less thanatmospheric in accordance with the wing angle of attack, a conduitwithin said wing and opening to the atmosphere at said zone, saidconduit extending to said quarters, a check valve in said conduitpermitting airflow only from said quarters toward the wing opening, andaural signalling means operated by airflow in said conduit at the crewquarters end of said conduit.

2. In aircraft including a wing having a zone at the' leading edgethereof subject to pressure greater or less than atmospheric inaccordance with the wing angle of attack, signalling means for warningof high angle of attack including a device in said zone and meansresponsive to the presence of pressure less than atmospheric at saiddevice for signalling the aircraft crew.

3. In aircraft, a wing having an opening at the upper part of theleading edge thereof, a conduit within said wing connecting with saidopening, signal means associated with said conduit operated by airfiowtherethrough, and means for limiting airflow in said conduit to a singledirection.

4. In aircraft including a member having a zone subject to less thanatmospheric or more than atmospheric pressure according to the aircraftangle of attack, signalling means, and means responsive only to thepressure less than atmospheric pressure at said zone for Operating saidsignalling means.

5. In aircraft including amember having a zone subject to less thanatmospheric or more than atmospheric pressure according to the angle ofattack of the aircraft, airflow operated signal- .ling means, and meansresponsive to less than atmospheric pressure at said zone forestablishing airflow for the operation of said signalling means.

6. In 'aircraft including a member having a zone subject to pressurechange between more than atmospheric and less than atmospheric thereonin accordance with the aircraft angle of attack, an indicator, and meansresponsive to pressure less than atmospheric at said zone for operatingsaid indicator.

7. In aircraft including a member having a zone subject to pressurechanges between more than atmospheric and less than atmospheric thereonin accordance with the aircraft angle of' attack, means subjecttopressure differencas occurring at said zone, and an indicator connectedwith said means and responsive in its indication to pressure less thanatmospheric at said zone. RAYMOND P. HOLLAND, JR.

